linux-kernel - Re: [PATCH 01/11] kexec_file: allow archs to handle special regions while locating memory hole

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Message-ID: <0e145e84-a6cf-4da3-1a1a-331a7e1ac1fa@linux.ibm.com>
Date:   Thu, 2 Jul 2020 00:01:31 +0530
From:   Hari Bathini <hbathini@...ux.ibm.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     Pingfan Liu <piliu@...hat.com>, Petr Tesarik <ptesarik@...e.cz>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH 01/11] kexec_file: allow archs to handle special regions
 while locating memory hole



On 01/07/20 1:16 pm, Dave Young wrote:
> On 06/29/20 at 05:26pm, Hari Bathini wrote:
>> Hi Petr,
>>
>> On 29/06/20 5:09 pm, Petr Tesarik wrote:
>>> Hi Hari,
>>>
>>> is there any good reason to add two more functions with a very similar
>>> name to an existing function? AFAICS all you need is a way to call a
>>> PPC64-specific function from within kexec_add_buffer (PATCH 4/11), so
>>> you could add something like this:
>>>
>>> int __weak arch_kexec_locate_mem_hole(struct kexec_buf *kbuf)
>>> {
>>> 	return 0;
>>> }
>>>
>>> Call this function from kexec_add_buffer where appropriate and then
>>> override it for PPC64 (it roughly corresponds to your
>>> kexec_locate_mem_hole_ppc64() from PATCH 4/11).
>>>
>>> FWIW it would make it easier for me to follow the resulting code.
>>
>> Right, Petr.
>>
>> I was trying out a few things before I ended up with what I sent here.
>> Bu yeah.. I did realize arch_kexec_locate_mem_hole() would have been better
>> after sending out v1. Will take care of that in v2.
> 
> Another way is use arch private function to locate mem hole, then set
> kbuf->mem, and then call kexec_add_buf, it will skip the common locate
> hole function.

Dave, I did think about it. But there are a couple of places this can get
tricky. One is ima_add_kexec_buffer() and the other is kexec_elf_load().
These call sites could be updated to set kbuf->mem before kexec_add_buffer().
But the current approach seemed like the better option for it creates a
single point of control in setting up segment buffers and also, makes adding
any new segments simpler, arch-specific segments or otherwise.

Thanks
Hari